Commons is the central repository of media files used by all the projects and all the languages of the Wikimedia Foundation. It currently has some 4,8 million freely usable media files.
Commons as a project is to be used in all our languages. That is a big issue and, it is an issue that is being addressed with all kinds of nifty template magic. In these templates texts are hidden and these texts are translated by Commons volunteers.
It was suggested on Commons to use the translatewiki.net functionality and community for the localisation of all these messages. As a result a great conversation started on IRC. A great conversation because it was to the point and practical.
An example message file was prepared by Siebrand, Multichil started defining messages and they are talking about the standards that are to be used. The delivery of the messages will be left to the LocalisationUpdate extension that is being worked on at the moment.
There will be around 2000 messages. It is unlikely that they will be part of the messages that will have to be localised for secondary projects... Obviously it is a good idea to localise them anyway :)